1. Field of the Invention
This invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium comprising a substrate of a non-magnetic material and a magnetic recording layer of a magnetic material provided thereon having an axis of easy magnetization vertical to the magnetic recording layer.
2. Description of the Prior Art
In the conventional magnetic recording method wherein a ring-shaped magnetic head is used, mainly utilized is the magnetization in the direction of movement of a recording medium (viz., magnetization of the longitudinal direction of the recording medium). Therefore, as the packing density of the signal to be recorded on the recording medium increases, the strength of the diamagnetic field in the recording medium increases and the residual magnetization is apt to be demagnetized and looped. As the result of the demagnetization and loop of the residual magnetization, it becomes difficult or impossible to reproduce the signal.
In order to make it possible to magnetically record information at a high density, there has been proposed a magnetic recording method using a magnetic recording medium comprising a substrate of a non-magnetic material and a magnetic recording layer of a magnetic material provided thereon having an axis of easy magnetization vertical to the magnetic recording layer. In the above-mentioned type magnetic recording method (hereinbelow referred to as "vertical magnetic recording method"), there is used a magnetic head comprising a rodshaped iron core and a coil wound up therearound. The magnetic head is located above the magnetic recording medium such that the iron core stands vertical to the medium with one end thereof close to the magnetic recording layer of the medium. Magnetic recording of information on the medium is performed by magnetizing the magnetic recording layer with a magnetic flux which is emanated from the iron core excited by the coil and flows vertical to the magnetic recording layer of the medium.
In the vertical magnetic recording method, magnetic recording is performed by utilizing a residual magnetization vertical to the magnetic recording layer of the medium. Therefore, as the packing density increases, the strength of the diamagnetic field in the medium decreases, and accordingly the strength of the residual magnetization increases. Thus, by employing the vertical magnetic recording method, the magnetic recording can be performed at a high density.
In the vertical magnetic recording method, the magnetic flux emanated from the iron core diverges and flows toward the medium. Further, when passing through the magnetic recording layer, the magnetic flux further diverges along the layer and the cross-sectional area of the magnetic flux becomes larger than that of the iron core. Therefore, the magnetized area of the magnetic recording layer becomes larger than the cross-sectional area of the iron core.
In order to solve the above-mentioned defect of the vertical magnetic recording method, Japanese Patent Laid Open No. 32,009/1978 proposes the provision of a magnetic pole of high permeability material on the opposite side of the medium to the magnetic head, thereby converging the magnetic flux from the iron core of the magnetic head.
Since the magnetic flux from the iron core is converged by the magnetic pole, the method disclosed in the Japanese Patent Laid Open No. 32,009/1978 has the advantage that magnetic recording can be performed at a high density. However, the method has the defect that the method is only applicable to the magnetic recording apparatus employing a magnetic recording tape, because the magnetic pole and the magnetic head should be located on the opposite sides of the medium. Further, the method has the defect that the magnetic recording apparatus should have a large size.